Heat transfer system including tubing with nucleation boiling sites

ABSTRACT

A heat transfer system includes a steam chamber that communicates in an open-loop arrangement with a first steam source for supplying steam to the steam chamber, the steam chamber including a steam exit for supplying steam to air at atmospheric pressure. A heat transfer tube communicates in a closed-loop arrangement with a second steam source for supplying steam to an interior surface of the heat transfer tube, the heat transfer tube vaporizing condensate forming within the heat transfer system back to steam that is supplied to the air via the steam exit. The outer surface of the heat transfer tube is configured to contact the condensate and vaporize the condensate back into steam, wherein the heat transfer tube includes a plurality of pockets formed on the outer surface of the tube, each pocket including a pocket exit/entry portion having a smaller cross-sectional area than the cross-sectional area of the pocket at a root portion thereof adjacent the outer surface of the tube.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/148,150, filed Oct. 1, 2018; which is a continuation of U.S. patentapplication Ser. No. 15/283,580, filed Oct. 3, 2016, now abandoned;which is a continuation of U.S. patent application Ser. No. 13/939,808,filed Jul. 11, 2013, now U.S. Pat. No. 9,459,055; which is acontinuation of U.S. patent application Ser. No. 12/270,582, filed Nov.13, 2008, now U.S. Pat. No. 8,505,497; which claims the benefit of U.S.Provisional Patent Application Ser. No. 61/003,142, filed Nov. 13, 2007,which applications are hereby incorporated by reference in theirentirety.

TECHNICAL FIELD

The principles disclosed herein relate generally to metallic heattransfer tubes including nucleate boiling sites on outer surfacesthereof and uses thereof in various heat transfer applications,particularly in humidification steam dispersion applications.

BACKGROUND

In submerged chiller refrigerating applications, the outside of a heattransfer tube is normally submerged in a refrigerant to be boiled, whilethe inside conveys liquid, usually water, which is chilled as it givesup its heat to the tube and refrigerant. In a boiling application suchas a refrigerating application, it is desirable to maximize the overallheat transfer coefficient.

In order to maximize the heat transfer coefficient, it is known to makemodifications to the outside surface of a heat transfer tube in order totake advantage of the phenomenon known as “nucleate boiling”. Accordingto one example, the outer surface of a heat transfer tube may bemodified to produce multiple pockets (i.e., cavities, openings,enclosures, boiling sites, or nucleation sites) which functionmechanically to permit small vapor bubbles to be formed therein. Thevapor bubbles tend to form at the base or root of the nucleation siteand grow in size until they break away from the outer surface. Uponbreaking away, additional liquid takes the vacated space and the processis repeated to form other vapor bubbles. In this manner, the liquid isboiled off or vaporized at a plurality of nucleate boiling sitesprovided on the outer surface of the metallic tubes.

According to one example, the external enhancement is provided bysuccessive cross-grooving and rolling operations performed after finningof the tubes. The finning operation, in a preferred embodiment fornucleate boiling, produces fins while the cross-grooving and rollingoperation deforms the tips of the fins and causes the surface of thetube to have the general appearance of a grid of generally flattenedblocks. The flattened blocks are wider than the fins and are separatedby narrow openings between the fins. The roots of the fins and thecavities or channels formed therein under the flattened fin tips are ofmuch greater width than the surface openings so that the vapor bubblescan travel outwardly through the cavity and through the narrow openings.The cavities and narrow openings and the grooves all cooperate as partof a flow and pumping system so that the vapor bubbles can readily becarried away from the tube and so that fresh liquid can circulate to thenucleation sites.

It is desirable to use heat transfer tubes having surface enhancementsin the form of nucleation sites in other types of heat transferapplications where maximizing the overall heat transfer coefficient isimportant.

SUMMARY

The principles disclosed herein relate to a heat transfer system thatincludes a humidification steam dispersion system comprising a steamchamber configured to communicate in an open-loop arrangement with afirst steam source for supplying steam to the steam chamber, wherein thesteam chamber includes a steam exit for supplying steam to air atatmospheric pressure and a heat transfer tube configured to communicatein a closed-loop arrangement with a second steam source for supplyingsteam to the heat transfer tube, wherein the heat transfer tube isconfigured to vaporize condensate forming within the heat transfersystem back to steam supplied to the air via the steam exit. The heattransfer tube is configured to contact the condensate and vaporize thecondensate back into steam. The heat transfer tube includes a pluralityof nucleation boiling sites that are formed by pockets defined on anouter surface of the tube, the pockets including pocket exit/entryportions (i.e., pores) having a smaller cross-sectional area than thecross-sectional area of the pockets at the root portions adjacent theouter surface of the tube.

According to another aspect of the disclosure, the disclosure is relatedto a heat transfer system that includes a humidification steamdispersion system that uses a higher pressure steam heat exchangerwithin a lower pressure steam humidification chamber to pipe unwantedcondensate away from the steam humidification chamber, wherein the steamheat exchanger forms a closed loop arrangement with a pressurized steamsource and the steam heat exchanger includes a heat transfer tubecomprising nucleate boiling sites defined on the outer surface of thetube for boiling the condensate.

A variety of additional inventive aspects will be set forth in thedescription that follows. The inventive aspects can relate to individualfeatures and combinations of features. It is to be understood that boththe foregoing general description and the following detailed descriptionare exemplary and explanatory only and are not restrictive of the broadinventive concepts upon which the embodiments disclosed herein arebased.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view of a heat transfer system having featuresthat are examples of inventive aspects in accordance with the principlesof the present disclosure;

FIG. 2 is a perspective view illustrating a portion of the heat transfersystem of FIG. 1, wherein a portion of a central steam dispersionmanifold has been cut-away to expose the internal features thereof;

FIG. 3 is an enlarged, partially broken away axial cross-sectional viewof a heat transfer tube suitable for use in the heat transfer system ofFIG. 1; and

FIG. 4 is a schematic depiction of the outer surface of the tube of FIG.3.

DETAILED DESCRIPTION

A heat transfer system 5 having features that are examples of inventiveaspects in accordance with the principles of the present disclosure isillustrated in FIGS. 1 and 2. In the present disclosure, the heattransfer system 5 is depicted as a humidification steam dispersionsystem 10. As will be described in greater detail below, the steamdispersion system 10 utilizes a heat transfer tube 11 that includesnucleate boiling sites on an outer surface thereof, wherein the tube 11is used for boiling unwanted condensate/water off portions of the steamdispersion system 10. The heat transfer tube 11 used in the steamdispersion system 10 includes a plurality of pockets defined on an outersurface of the tube, the pockets including pocket exit/entry portions 50(i.e., pores) having smaller cross-sectional areas than thecross-sectional areas of the pockets at the root portions thereof,adjacent the outer surface of the tube 11.

It is desirable in a system such as the steam dispersion system 10 shownin FIGS. 1 and 2 to efficiently vaporize condensate/water formed onparts of the system 10. In a humidification process, steam is normallydischarged from a steam source as a dry gas. As steam mixes with coolerair (e.g., duct air), some condensation takes place in the form of waterparticles. Within a certain distance, the water particles are absorbedby the air stream. The distance wherein water particles are completelyabsorbed by the air stream is called absorption distance. Before thewater particles are absorbed into the air within the absorptiondistance, water particles collecting on steam dispersion equipment mayadversely affect the life of such equipment. Thus, a short absorptiondistance is desired.

It should be noted that a humidification steam dispersion system such asthe one illustrated and described herein is simply one example of a heattransfer system wherein a heat transfer tube defining nucleate boilingsites on an outer surface thereof may be used for boiling or vaporizingcondensate/water. Heat transfer systems having other configurationswherein tubes with nucleate boiling sites are used for condensate orwater boiling purposes are certainly possible and are contemplated bythe inventive features of the present disclosure.

In FIG. 1, the steam dispersion system 10 is shown diagrammatically. InFIG. 2, a portion of the steam dispersion system 10 is shown. FIG. 2shows a central steam manifold 16 with a plurality of steam dispersiontubes 18 extending therefrom, wherein a portion of the central steammanifold 16 has been cut-out to expose and illustrate a heat exchanger20 therein. As will be discussed in further detail, the heat exchanger20 is formed from a heat transfer tube that defines nucleate boilingsites on an outer surface thereof. The heat transfer tube 11 is shown ingreater detail in FIGS. 3 and 4.

Still referring to FIGS. 1 and 2, the steam dispersion system 10includes a steam dispersion apparatus 12 and a steam source 14. Thesteam source 14 may be a boiler or another steam source such as anelectric or gas humidifier. The steam source 14 provides pressurizedsteam towards the manifold 16 of the steam dispersion apparatus 12. Inthe depicted example, the pressurized steam passes through a modulatingvalve 8 for reducing the pressure of the steam from the steam source 14to about atmospheric pressure before it enters the manifold 16. Steamdispersion tubes 18 coming out of the manifold 16 disperse the steam tothe atmosphere at atmospheric pressure.

In the embodiment illustrated in FIGS. 1 and 2, the manifold 16 isdepicted as a header 17. A header is generally understood in the art torefer to a manifold that is designed to distribute pressure evenly amongthe tubes protruding therefrom.

In accordance with the steam dispersion system 10 of FIGS. 1 and 2, thesteam source 14 also supplies steam to the heat exchanger 20 (i.e.,evaporator) located within the header 17. The steam supplied to the heatexchanger 20 is piped through a continuous loop with the steam source14. The steam supplied by the steam source 14 is piped through thesystem 10 at a pressure generally higher than atmospheric pressure,which is normally the pressure within the header 17. In this manner,pumps or other devices to pipe the steam through the system 10 may beeliminated.

Although illustrated as being the same, it should be noted that thesteam source supplying steam to the header 17 and the steam sourcesupplying steam to the heat exchanger 20 may be two different sources.For example, the source that supplies humidification steam to the header17 may be generated by a boiler or an electric or gas humidifier whichoperates under low pressure (e.g., less than 1 psi.). In otherembodiments, the source that supplies humidification steam to the header17 may be operated at higher pressures, such as between about 2 psi and60 psi. In other embodiments, the humidification steam source may be runat higher than 60 psi. The humidification steam that is inside theheader 17 ready to be dispersed is normally at about atmosphericpressure when exposed to air.

The pressure of the heat exchanger steam is normally higher than thepressure of the humidification steam. The heat exchanger steam sourcemay be operated between about 2 psi and 60 psi and is configured toprovide steam at a pressure higher than the pressure of thehumidification steam to be dispersed. The heat exchanger steam sourcemay be operated at pressures higher than 60 psi.

Although in the depicted embodiment, the internal heat exchanger 20 isshown as being utilized within a header, it should be noted that theheat exchanger 20 of the system 10 can be used within any type of acentral steam chamber that is likely to encounter condensate, eitherfrom the dispersion tubes 18 or other parts of the system 10. A headeris simply one example of a central steam chamber wherein condensatedripping from the tubes 18 is likely to contact the heat exchanger 20.

FIG. 2 illustrates in detail the steam dispersion apparatus 12 of thesteam dispersion system 10 of FIG. 1. The steam dispersion apparatus 12includes the plurality of steam dispersion tubes 18 extending from thesingle header 17. The header 17 receives steam from the steam source 14and the steam is dispersed into air (e.g., duct air) through nozzles 22of the steam tubes 18. As discussed above, the humidification steaminside the header 17 communicating with the tubes 18 may be atatmospheric pressure, generally at about 0.1 to 0.5 psi and at about 212degrees F. In other embodiments, the steam inside the header 17 may beat less than 1 psi.

Still referring to FIG. 2, in the embodiment of the dispersion system10, the steam dispersion apparatus 12 includes the heat exchanger 20within the header 17. In the depicted embodiment, the heat exchanger 20is formed from continuous closed-loop piping that communicates with thesteam source 14. The portion of the heat exchanger 20 within the header17 includes a U-shaped configuration 24 that generally spans the fulllength of the header 17. In the depicted embodiment, the steam heatexchanger 20 is generally located at a bottom portion of the header 17.Steam at steam source pressure (e.g., boiler pressure) is supplied tothe heat exchanger 20 and enters the heat exchanger 20 via an inlet 26.As discussed above, the steam entering the heat exchanger 20 maygenerally be at about 2-60 psi and at about 220-310 degrees F. Incertain embodiments, the steam provided by the steam source 14 may be atabout 15 psi. In certain other embodiments, the steam provided by thesteam source 14 may be at about 5 psi. In other embodiments, the steamprovided by the steam source 14 may be at no less than about 2 psi. Inyet other embodiments, the steam provided by the steam source may be atmore than 60 psi. The steam within the heat exchanger 20 is pipedtherethrough and exits the heat exchanger 20 through an outlet 28.

Although the heat exchanger 20 is depicted as a U-shaped tube accordingto one embodiment, other types of configurations that form a closed-loopwith the steam source 14 may be used. Additionally, the tube 11 formingthe heat exchanger 20 may take on various profiles. According to oneembodiment, the tube of the heat exchanger 20 may have a roundcross-sectional profile. The steam heat exchanger 20 may be made fromvarious heat-conductive materials, such as metals. Metals such ascopper, stainless steel, etc., are suitable for the heat exchanger 20.

As discussed above, according to the inventive features of thedisclosure, the heat exchanger 20 is made from a tube that includes aplurality of nucleate boiling sites defining pockets on the outersurface of the tube. After formation, the pockets define pocketexit/entry portions 50 having smaller cross-sectional areas than thecross-sectional areas of the pockets at the root portions thereof,adjacent the outer surface of the tube 11. The nucleate boiling sitesassist in vaporizing condensate at a higher efficiency than with tubeshaving smooth exterior surfaces.

One embodiment of a heat transfer tube 11 defining nucleate boilingsites on the outer surface that is suitable for use with the steamdispersion system 10 is shown in FIGS. 3 and 4.

Referring now to FIG. 3, in the depicted embodiment, the tube 11comprises a deformed outer surface indicated generally at 32 and adeformed inner surface indicated generally at 34. According to oneexample, the tube 11 of the FIGS. 3 and 4 may have a nominal outerdiameter of about ¾ inches. According to another embodiment, the tubemay have an outer diameter of about 1 inch. According to yet anotherembodiment, the tube may have an outer diameter of about ⅝ inches.

According to the depicted embodiment, the inner surface 34 of tube 11comprises a plurality of helically formed ridges, indicated by referencenumerals 36, 36′, 36″ (generically referred to as ridges 36). Ridges 36define a pitch “p”, a ridge width “b” (as measured axially at the ridgebase), and an average ridge height “e”. A helix lead angle θ is measuredfrom the axis of the tube.

According to one embodiment, the tube 11 shown in FIG. 3 includesthirty-four ridge starts, a pitch of 0.0516 inches, and a ridge helixangle of 49 degrees. These parameters of the tube 11 enhance the insideheat transfer coefficient of the tube by providing increased surfacearea. It should be noted that these parameter values are only exemplaryand other values may certainly be used depending upon the heat transfercharacteristics desired.

As discussed above, the outer surface 32 of the tube 11 is deformed toproduce nucleate boiling sites. In order to form the nucleate boilingsites, first, a plurality of fins 38 are provided on the outer surface32 of tube 11. Fins 38 may be formed on a conventional arbor finningmachine. The number of arbors utilized depends on such manufacturingfactors as tube size, throughput speed, etc. The arbors are mounted atappropriate degree increments around the tube 11, and each is preferablymounted at an angle relative to the tube axis. The finning disks form aplurality of adjacent, generally circumferential, relatively deepchannels 40 (i.e., first channels), as shown in FIGS. 3 and 4.

After fin formation, outer surface 32 of tube 11 is notched (i.e.,grooved) to provide a plurality of notches 56 forming relatively shallowchannels 42 (e.g., second channels), as shown in FIG. 4. The notchingmay be accomplished using a notching disk as known in the art. As shownin FIG. 4, second channels 42 interconnect adjacent pairs of firstchannels 40 and are positioned at an angle to the first channels 40.

After notching, fins 38 are compressed using a compression diskresulting in flattened fin heads 44. The appearance of the tube outersurface 32 after compression with flattened fin heads 44 is shown in aplan view in FIG. 4. The cross-sectional appearance is shown in FIG. 3.

According to one embodiment, a typical notch depth, into the fin tip,before any flattening is performed, is about 0.015 inches. According tothe same embodiment, after flattening, the depth measured from the finaloutside surface is about 0.005 inches. According to one embodiment, thenotches 56 are spaced around a circumference of each fin 38 at a pitchwhich is in a range of between 0.0161 to 0.03 (as measured along thecircumference of fin 38 at a base of the notches), and preferably in arange of 0.020 inches to 0.025 inches. Adjacent notches 56 arenon-contiguously spaced apart so that a flattened fin 44 is intermediateneighboring pores 50.

Referring back to FIG. 4, pores 50 are shown as being at theintersection of the first channels 40 and the second channels 42 andbeing at the bottom of the second channels 42. Each pore 50 (i.e., thereduced cross-sectional portion of a pocket) defines a pore size (e.g.,cross-sectional area), which is the size of the opening from the boilingor nucleation site from which vapor escapes to a water bath. Accordingto one embodiment, the fins 38 are so spaced, and channels 42 so formed,whereby pores 50 have an average area less than 0.00009 square inches.Preferably, the pore average sizes for tube 11 are between 0.000050square inches and 0.000075 square inches.

According to one embodiment, the pores 50 have a density of about atleast 2000 per square inch of tube outer surface 32. Preferably, thepore density exceeds 3000 per square inch and is on the order of about3112 pores per square inch according to a preferred embodiment. Thenumber of pores per square inch depends on tube wall thickness under thefins. With the preferred 3112 number of pores, for example, a wallthickness of 0.025 inches may be present. If a tube with a 0.035 inch orheavier wall was manufactured, the fin count would tend to increase. Inreferring to pore average cross-sectional area, it is recognized thatfabrication techniques such as finning may result in some pore sizesbeing greater than 0.00009 square inches. However, a vast majority ofthe pores depicted herein have an average area of less than 0.00009square inches.

According to one embodiment, the spacing of the fins 38 of the tube 11of FIGS. 3 and 4 is sixty-one fins per inch. Thus, according to the sameembodiment, the plurality of helical fins 38 are axially spaced at apitch less than 0.01754 inches (i.e., more than fifty-seven fins/in),and preferably less than 0.01667 inches (i.e., more than sixty fins/in).

Factors such as the notch pitch and number of fins per inch influencethe number of pores per square inch on the outside surface of the tube.

The tube 11 has mechanical enhancements which can individually improvethe heat transfer characteristics of either the tube outer surface 32 orthe tube inner surface 34, or which can cooperate to increase theoverall heat transfer efficiency between the outer surface 32 and theinner surface 34. The tube internal enhancement, which comprises theplurality of closely spaced helical ridges 36, provides increasedsurface area. The tube external enhancement, which is provided bysuccessive grooving and compression operations performed after a finningoperation, assists in nucleate boiling. The finning operation producesfins 38 while the grooving (e.g., notching) and compression operationscooperate to flatten tips of fins 38 and cause the outer surface 32 ofthe tube 11 to have the general appearance of a grid of generallyflattened ellipses, as shown in FIG. 4.

Between pores 50, underneath flattened tips 44 of fins 38, each channel40 defines a channel segment 40 s, as shown in FIG. 4, which is enclosedfrom above by the flattened tips 44 of fins 38. The flattened ellipsesare wider than pre-compressed fins 38. After formation, the flattenedellipses end up being separated by narrow openings 54 between fins 38and by the first channels 40 that are at an angle thereto. The roots ofthe fins 38 and the channels 40 formed therein under the flattened fintips 44 are of greater width than the pores 50, so that vapor bubblescan be formed at nucleation sites in the cavities/pockets (e.g., beneathpores 50) and then travel outwardly from cavities formed by channels 40and through the narrow pores 50. Pores 50 are shown (partially coveredby notched and flattened fins) in FIG. 4. The cavities and narrowopenings and the grooves all cooperate as part of a flow and pumpingsystem so that the vapor bubbles can be formed and readily carried awayfrom the tube 11 and so that fresh liquid can circulate to thenucleation sites. The rolling operation is performed in a manner suchthat the cavities produced will be in a range of sizes with a sizedistribution predominately of the optimum size for nucleate boiling of aparticular fluid (such as water according to the present disclosure)under a particular set of operating conditions.

Thus, in accordance with the present disclosure, a heat transfer tube isformed which includes surface enhancements of both its inner and outertube surfaces, and which can be produced in a single pass in aconventional finning machine.

The heat transfer tube 11 illustrated in FIGS. 3 and 4 and describedherein is described in further detail in U.S. Pat. No. 5,697,430,incorporated by reference herein in its entirety. Other configurationsof heat transfer tubes suitable for the heat transfer system disclosedherein that include nucleate boiling sites formed by pockets defined onan outer surface of the tube wherein the pockets include pocketexit/entry portions having a smaller cross-sectional area than thecross-sectional area of the pockets at the root portions adjacent theouter surface of the tube are described in U.S. Pat. Nos. 4,660,630;3,768,290; 3,696,861; 4,040,479; 4,438,807; 7,178,361; 7,254,964, theentire disclosures of which are incorporated herein in their entireties.

Now referring back to FIGS. 1 and 2, in operation of the heat transfersystem 5, dispersed humidification steam condenses inside the steamdispersion tubes 38 when encountering cold air, for example, within aduct. Condensate 30 that forms within the dispersion tubes 18 drips downvia gravity toward the heat exchanger 20 located at the bottom of theheader 17. The condensate 30 contacts the exterior surface of the tubeof the heat exchanger 20 and is vaporized (i.e., reflashed back into thesystem). The energy required to turn the fallen condensate 30 back intosteam creates condensate within the heat exchanger 20. The energy tovaporize the condensate comes from condensing an equivalent mass ofsteam within the heat exchanger 20. However, since the interior of theheat exchanger 20 is under a higher pressure, i.e., the pressure of thesteam source 14, the condensate created therewithin is moved through thesystem 10 under this higher pressure, without the need for pumps orother devices.

In the depicted embodiment, the heat exchanger 20 is shown to spangenerally the entire length of the header 17 so that it can contactcondensate 30 dripping from all of the tubes 18. In other embodiments,the heat exchanger 20 may span less than the entire length of the header(e.g., its length may be ½ of the header length or less).

It should be noted that the heat exchanger 20 could be located at adifferent location than the interior of a header 17. The interior of theheader 17 is one example location wherein condensate 30 forming withinthe steam dispersion system 10 may eventually collect. Other locationsare certainly possible, so long as the steam within the heat exchanger20 is at a higher pressure than atmospheric pressure and so long as thecondensate forming within the heat exchanger 20 is able to contact theheat exchanger 20 for piping through the system 10. Please refer to U.S.Pat. No. 8,534,645, the entire disclosure of which is incorporatedherein by reference, for further configurations of steam dispersionsystems utilizing a heat exchanger such as the heat exchanger 20 shownin the present disclosure.

With the configuration of the steam dispersion system 10 of the presentdisclosure, the resulting condensate may be moved efficiently throughthe system 10 without the use of pumps or other devices.

As noted previously, a humidification steam dispersion system such asthe one illustrated and described herein is simply one exampleconfiguration of a heat transfer system wherein a heat transfer tubedefining nucleate boiling sites on an outer surface thereof may be usedto boil or vaporize condensate/water. Other heat transfer systemconfigurations are certainly possible and are contemplated by theinventive features of the present disclosure.

For example, according to another example heat transfer system, a heatexchanger defining nucleate boiling sites on an outer surface thereofmay be used within a chamber that holds water, wherein the water wouldbe boiled by steam running through the heat exchanger. The vaporizedwater would then be dispersed as humidification steam through a steamoutlet of the chamber. In such a steam dispersion system, instead of thechamber receiving humidification steam directly from a steam source suchas a boiler, clean, chemical-free water could be used within the chamberfor creating the humidification steam.

Other systems such as those described above, wherein a heat transfertube defining nucleate boiling sites on an outer surface thereof is usedto boil or vaporize condensate/water are certainly possible andcontemplated by the inventive features of the present disclosure.

The above specification, examples and data provide a completedescription of the inventive features of the disclosure. Manyembodiments of the disclosure can be made without departing from thespirit and scope thereof.

1. A heat transfer system comprising: a steam chamber configured tocommunicate in an open-loop arrangement with a first steam source forsupplying steam to the steam chamber, the steam chamber including asteam exit for supplying steam to air at atmospheric pressure; and aheat transfer tube configured to communicate in a closed-looparrangement with a second steam source for supplying steam to aninterior surface of the heat transfer tube, the heat transfer tubeconfigured to vaporize condensate forming within the heat transfersystem back to steam that is supplied to the air via the steam exit,wherein an outer surface of the heat transfer tube is configured tocontact the condensate and vaporize the condensate back into steam, theheat transfer tube including a plurality of pockets formed on the outersurface of the tube, each pocket including a pocket exit/entry portionhaving a smaller cross-sectional area than the cross-sectional area ofthe pocket at a root portion thereof adjacent the outer surface of thetube.
 2. A heat transfer system according to claim 1, wherein the steamchamber includes a header and the plurality of steam dispersion tubesprotruding out of the header, the heat transfer tube located within theheader.
 3. A heat transfer system according to claim 1, wherein the heattransfer tube includes helical ridges formed on the interior surface ofthe tube.
 4. A heat transfer system according to claim 1, wherein theheat transfer tube is made out of copper.
 5. A heat transfer systemaccording to claim 1, wherein the first steam source and the secondsteam source are the same source.
 6. A heat transfer system according toclaim 1, wherein the heat transfer tube is mounted outside of the steamchamber.
 7. A heat transfer system according to claim 1, wherein atleast one of the first steam source and the second steam source providessteam at a pressure of about 2 psi to about 60 psi.
 8. A heat transfersystem according to claim 1, wherein the second steam source isconfigured to supply steam to the heat transfer tube at a pressurehigher than atmospheric pressure.
 9. A heat transfer system according toclaim 1, wherein the density of the pockets formed on the outer surfaceof the tube is at least 2000 pockets per square inch.
 10. A heattransfer system according to claim 1, wherein the cross-sectional areaof the pocket exit/entry portion is less than about 0.000090 squareinches.
 11. A heat transfer system according to claim 10, wherein thecross-sectional area of the pocket exit/entry portion is between about0.000050 and 0.000075 square inches.
 12. A heat transfer systemaccording to claim 1, wherein an outer diameter of the heat transfertube is about 1 inch.